Pigment concentrates for blending in thermoplastic resins are known. Such concentrates must be selected according to the characteristics of the resins to be colored. It is desirable to avoid defects in colored resins, particularly those which are transparent or translucent. For example, certain polymodal branched block copolymers of butadiene and styrene are disclosed in my previous U.S. Pat. No. 3,939,112 (1976). These resinous copolymers, marketed by the Phillips Petroleum Company as K-Resin.RTM. resins, have many desirable properties, one of which is optical clarity.
It is often desired to provide coloration to articles made from such resins while still maintaining transparency, though opaque or "semi-opaque" colored articles made from various resins are also useful in many applications. In any case, a well known convenient method of providing colored thermoplastic compositions is to employ a pigment concentrate or masterbatch wherein a pigment or colorant at relatively high concentration is admixed with a polymer which is highly compatible with the thermoplastic resin to be colored. For example, polystyrene, as the polymer to prepare the pigment concentrate, does not harm the transparency of the final blend of compositions based upon such polymodal branched block copolymers, but the physical properties such as impact strength are significantly reduced. To ensure compatibility, it would be highly desirable to employ a similar polymer to prepare the pigment concentrate to be further blended or "let down" with the base polymer.
Thus, it is desirable to develop pigment concentrates comprising resinous polymers or similar resins which can be admixed with a major portion of the same, a similar or related resin without creating the problems such as defects in esthetic appearance or physical properties.
Problems have been encountered in attempting to use certain polymodal branched block copolymers in pigment concentrates for coloring similar polymers. Primarily, gels or opaque surface blemishes are generated in the final articles. In addition, agglomerates of pigment particles which have not been well dispersed often appear and mar the appearance of the final articles. Akin to the agglomerate problem is the problem of streaking wherein the final article shows streaks of heavier or lighter coloration. Streaking is generally an undesirable feature in the final articles. These defects are particularly conspicuous and objectionable in clear colored resins, which are a significant application of K-Resin.RTM. resins and similar polymodal copolymers.
Possible explanations for the above problems are as follows: (1) Gels are caused by the high shear conditions needed to obtain a reasonably homogeneous blend of the pigment and resin in the concentrate; (2) Pigment agglomerates result from poorly dispersed pigment which in turn might result from inadequate mixing in preparing the concentrate; and (3) Streaks are believed to result from inadequate mixing of the pigment concentrate with the virgin polymer.
The instant invention provides a means to reduce the occurrence of the above problems in producing colored articles of various resinous polymers, such as polymodal resinous copolymers or similar resins by the use of certain additives in preparing a resinous pigment concentrate.
An object of this invention is to provide a resinous pigment concentrate which can be used to produce colored resinous copolymers or similar resins without adverse effects as described above. Another object of this invention is a process for preparing such a resinous pigment concentrate. Still another object is a process for coloring resinous copolymers or similar resins by admixing a base resin with the inventive resinous pigment concentrate. A further object of this invention is a process for producing articles of resinous copolymers or similar resins colored with the inventive pigment concentrate.
Other objects, advantages and features of the instant invention will be apparent from the following disclosure and the appended claims.